1. Field of the Invention
This invention relates to a clock reproducing apparatus and a data reproducing apparatus in a magnetic disc system such as a hard disc drive, etc.
2. Description of the Prior Art
An external clock type magnetic disc system is adapted to generate a clock signal synchronous with a data existing point which gives recording/reproduction timing of data on the basis of clock patterns discretely arranged at equal intervals on concentric or spiral recording tracks. Namely, by a phase synchronization loop (so called PLL) adapted to control the oscillating phase of a voltage controlled oscillator (VCO) based on phase error information obtained by detecting a peak existing time of a reproduced signal waveform of the above clock pattern by using a peak detector to sample and hold a saw-tooth wave at that time to carry out phase comparison thereof, a clock signal synchronous with the data existing point is reproduced.
In the conventional clock reproducing apparatus, since phase comparison is carried out on the basis of the clock pattern, a peak detector and a saw-tooth wave generator were used. These circuit elements are complicated analog signal processing circuits. Accordingly, so it was difficult to allow the circuit to become compact and/or to be adjustment-free. It was also difficult for such a clock reproducing circuit block to coexist with other circuit blocks within one LSI adapted for digital processing.